Vibration-sensitive transducer

Abstract

A transducer in the form of a long cable for producing electrical signals in response to mechanical vibration of the cable. The cable comprises an elongate magnetic member and an electrical conductor extending alongside the magnetic member, the electrical conductor being loosely mounted in the magnetic field of the magnetic member so that mechanical vibration of the cable causes the electrical conductor to move relative to the magnetic field whereby an e.m.f. and hence an electrical signal is induced in the conductor. The transducer may be used in monitoring or security apparatus.

I claim: 
     
       1. A cable type transducer in the form of an elongate cable for producing electrical signals in response to a mechanical vibration or impulse of the cable at any point along the cable comprising an elongate structure comprising elongate flexible magnetic flux generating means extending continuously longitudinally of said elongate structure, an electrical conductor and support means for supporting said electrical conductor so that it extends substantially longitudinally of the elongate structure and is loosely constrained laterally of the structure within the magnetic field generated by the magnetic flux generating means to allow limited movement of the electrical conductor relative to magnetic field generated by the magnetic flux generating means so that the said electrical conductor is movable in response to mechanical disturbance of the cable at any point along the cable, relative to the magnetic field generated by the magnetic flux generating means, so that the movement induces an e.m.f. in the electrical conductor thereby producing said electrical signals. 
     
     
       2. A cable type transducer according to claim 1 wherein the magnetic flux generating means is formed from a permanently magnetised metallic material. 
     
     
       3. A cable type transducer according to claim 1 wherein the magnetic flux generating means is formed from a permanently magnetised plastics material. 
     
     
       4. A cable type transducer according to claim 1 wherein the magnetic flux generating means is in the form of a tape. 
     
     
       5. A cable type transducer according to claim 1 further comprising a sheath and a wire loosely fitting into said sheath and wherein said electrical conductor is constituted by at least one run of said wire lengthwise of the cable. 
     
     
       6. A cable type transducer according to claim 5, wherein the sheath is integral with the magnetic flux generating means. 
     
     
       7. A cable type transducer according to claim 1 wherein the electrical conductor is disposed so as to be non-inductive with respect to an externally applied electro-magnetic field. 
     
     
       8. A cable type transducer according to claim 7 wherein the electrical conductor comprises two runs of electrical conductor arranged in a twisted pair configuration. 
     
     
       9. A cable type transducer according to claim 1 further comprising a further electrical conductor extending along the structure, the first mentioned electrical conductor and the further electrical conductor being connected so as to provide a balanced output. 
     
     
       10. A cable type transducer for producing electrical signals in response to a mechanical vibration or impulse comprising an elongate structure comprising elongate magnetic flux generating means and an electrical conductor, the electrical conductor being loosely retained alongside the magnetic flux generating means within the magnetic field generated thereby so that the said electrical conductor is movable in response to mechanical disturbance of the cable, relative to the magnetic flux generating means, so that the movement induces an e.m.f. in the electrical conductor thereby producing said electrical signals and wherein the magnetic flux generating means constitutes an additional electrical conductor and the first mentioned electrical conductor and the magnetic flux generating means are electrically connected so as to provide a differential output. 
     
     
       11. A cable type transducer for producing electrical signals in response to a mechanical vibration or impulse comprising an elongate structure comprising elongate magnetic flux generating means and an electrical conductor, the electrical conductor being loosely retained alongside the magnetic flux generating means within the magnetic field generated thereby so that the said electrical conductor is movable in response to mechanical disturbance of the cable, relative to the magnetic flux generating means, so that the movement induces an e.m.f. in the electrical conductor thereby producing said electrical signals, the transducer further comprising a cylindrical core having a longitudinally extending slot defined therein, and wherein the said electrical conductor is located in the slot in the periphery of the cylindrical core. 
     
     
       12. A cable type transducer according to claim 11, wherein the said core constitutes the said magnetic flux generating means. 
     
     
       13. A cable type transducer according to claim 12, wherein the core comprises two parts which when assembled meet on a diameter of the cross-section of the core. 
     
     
       14. A cable type transducer, according to claim 13, wherein at least one of the said slots is wholly defined in one of the parts of the core and at least one other of the said slots is defined by both parts of the core and straddles their common diameter plane. 
     
     
       15. A cable type transducer according to claim 11, wherein the said electrical conductor comprises a first run of said electrical conductor and a second run of said electrical conductor and the said longitudinally extending slots comprise one or more narrow slots and one or more wide slots, the width of the said narrow slots being smaller than the diameter of the said first run of electrical conductor and the width of the said wide slots being greater than the diameter of the said second run of said electrical conductor, the first run of said electrical conductor being housed in the said one or more narrow slots and the second run of conductor being housed in the said one or more wide slots, in that the second run of conductor is free to move relative to the magnetic flux generating means in response to the vibration of the cable but the first run of said electrical conductor is held fixed relative to the magnetic flux generating means. 
     
     
       16. A cable type transducer in the form of an elongate cable for producing electrical signals in response to a mechanical vibration or impulse of the cable at any point along the cable comprising an elongate structure comprising elongate flexible magnetic flux generating means extending continuously longitudinally of said elongate structure and formed by a tape of permanently magnetized material parallel to its width in the same direction over its enire length, an electrical conductor and support means for supporting said electrical conductor so that it extends substantially longitudinally of the elongate structure and is loosely retained alongside the edges of the tape of magnetic flux generating means adjacent a pole of the magnetic flux generating means within the magnetic field generated thereby to allow limited movement of the electrical conductor relative to the magnetic field generated by the magnetic flux generating means so that the said electrical conductor is movable in response to mechanical disturbance of the cable, relative to the magnetic field generated to the magnetic flux generating means, so that the movement induces an e.m.f. in the electrical conductor thereby producing said electrical signals, the support means comprising a hollow sheath extending alongside said magnetic flux generating means and said electrical conductor comprising a wire loosely fitting into said sheath, said wire having an external diameter smaller than an internal diameter of said hollow sheath and wherein said electrical conductor is constituted by at least one run of said wire lengthwise of the cable. 
     
     
       17. A cable type transducer for producing electrical signals in response to a mechanical vibration or impulse comprising an elongate structure comprising elongate magnetic flux generating means and an electrical conductor, the electrical conductor being loosely retained within the magnetic field generated by the magnetic flux generating means so that the said electrical conductor is movable in response to mechanical disturbance of the cable, relative to the magnetic flux generating means, so that the movement induces an e.m.f. in the electrical conductor thereby producing said electrical signals, the transducer further comprising a core conforming generally to a cylindrical surface and having means defining at least one slot portion extending longitudinally of the core and radially inwardly of said cylindrical surface and in which slot portion is located said loosely retained electrical conductor. 
     
     
       18. A cable type transducer according to claim 17 wherein the core comprises two parts having generally semi-circular cross-sections. 
     
     
       19. A cable type transducer according to claim 17 wherein the core constitutes said magnetic flux generating means and comprises two parts each having a curved surface of a generally semi-circular cross-section and arranged with their curved surfaces facing outwardly from a diameter plane of the core, and wherein said at least one slot portion is defined by both parts of the core and straddles said diameter plane. 
     
     
       20. A cable type transducer according to claim 19 wherein the core has first and second slot portions defined therein and said electrical conductor comprises a first run having a diameter smaller than the first slot portion and being loosely retained therein so that it is free to move in response to mechanical disturbance of the cable and a second run located in the second slot portion and being restrained against movement relative thereto. 
     
     
       21. A cable type transducer according to claim 20 wherein said second run of electrical conductor comprises a wire having a close-fitting insulating sheath.